In a gas supply unit in a semiconductor manufacturing apparatus, or the like, as shown in FIG. 13, conventionally, a pressure regulator R is provided in a gas supply line from a gas supply source SG and a plurality of branch pipe passages La, Lb, and Lc are provided to branch off a gas supply pipe passage Lo on the output side of the pressure regulator R. Additionally, automatic pressure regulators 5a, 5b, and 5c, respectively, composed of regulators 1a, 1b, and 1c, inlet side pressure sensors 2a, 2b, and 2c, outlet side pressure sensors 3a, 3b, and 3c, and controllers 4a, 4b, and 4c, and thermal type mass flow rate regulators MFC1, MFC2, and MFC3, are provided in the respective branch pipe passages La, Lb, and Lc. When pressure differences ΔP between the inlet side pressure sensors 2a, 2b, and 2c and the outlet side pressure sensors 3a, 3b, and 3c of the respective thermal type mass flow rate regulators MFC1, MFC2, and MFC3 are out of a range of set values, automatic control is performed so as to apply feedback to the regulators 1a, 1b, and 1c via the controllers 4a, 4b, and 4c, and the outlet side pressures of the respective regulators 1a, 1b, and 1c are regulated to bring the above-described pressure differences ΔP to be within the set values so that gas, at a set flow rate, may be stably supplied to respective targets 6a, 6b, and 6c that use the gas.
Furthermore, the control provided by the respective controllers 4a, 4b, and 4c is provided with characteristics of a so-called proportional-integral-derivative control action or “PID control action,” which is provided with an auto-tuning function that automatically tunes amounts of the respective control actions of a proportional control action (P control action), an integral control action (I control action), and a derivative control action (D control action) in order to promptly converge pressure differences (deviations) ΔP, between the inlet side pressure sensors 2a, 2b, and 2c and the outlet side pressure sensors 3a, 3b, and 3c, to zero in a shorter cycle.
The conventional automatic pressure regulators 5a, 5b, and 5c shown in FIG. 13 are capable of highly accurately controlling gas flow rates to be supplied to vacuum chambers serving as the target 6a, 6b, and 6c using gas, and are capable of relatively rapidly converging the gas flow rates to a new set flow rate even in the case where supply gas flow rates are changed, in order to provide an excellent practical utility.
However, there are many problems remaining to be solved in the automatic pressure regulators 5a, 5b, and 5c shown in FIG. 13. As one problem to be urgently solved, among those problems remaining, is the problem that, when the gas flow is made intermittent by the automatic pressure regulators 5a, 5b, and 5c at the time gas is supplied at a flow rate of approximately 10 to 1000 Standard Cubic Centimeters per Minute (SCCM) to the vacuum chambers 6a, 6b, and 6c (10−1 to 10−5 torr), so-called “overshoot” occurs in the flow rate on the outlet sides of the thermal type mass flow rate regulators MFC1, MFC2, and MFC3 at the start of gas supply, which brings about fluctuation in film density, film thickness, and the like, during semiconductor manufacturing. This results in difficulty with respect to forming films with a uniform film quality in a deposition system, or the like, in which the gas type to be supplied must be switched sharply.    Patent Document 1: Japanese Published Unexamined Patent Application No. 7-240375    Patent Document 2: Japanese Published Unexamined Patent Application No. 2005-339439